A cow chronically infected in one quarter with Staphylococcus aureus is a threat to herdmates and may pass the infection to them at milking. Yet some of these cows produce enough milk to encourage producers to keep them for a time. Some veterinarians and producers have used various methods to stop the milk production of the infected quarter, so the cow can remain in the herd without being such a great risk. Below is a summary of a study that compared two medications commonly used to stop milk production in one quarter (1). They concluded that the povidone-iodine combination worked best in this study.

A Washington State University study compared the ability of chlorhexidine and povidone-iodine to cause cessation of lactation in Staphylococcus aureus
infected mammary quarters, assess milk production in the treated quarter in the subsequent lactation, and evaluate whether microbiological cure was obtained.

Fourteen mid-to late-lactation Holstein-Friesian dairy cattle from the Washington State University dairy herd with single mammary quarter S. aureus intramammary infections were studied. Cows were randomly assigned to one of two treatment groups, povidone-iodine or chlorhexidine. Cows in the povidone-iodine group were infused with 120 ml of 5% povidone-iodine solution (0.5% iodine) after complete milk-out. Chlorhexidine-treated cows were infused with a proprietary chlorhexidine suspension after two milkings 24 h apart. Treated mammary quarters were not milked for the rest of the lactation. Milk production from each mammary quarter (kg of milk/quarter) was measured using in-line volume flow meters for 5 consecutive days before treatment and again at the start of the subsequent lactation.

Povidone-iodine caused permanent cessation of lactation in the treated quarter, whereas 71% of the chlorhexidine-treated mammary quarters returned to function in the subsequent lactation. Hence, if the primary objective is to eliminate further milk secretion from the mammary quarter, and thereby presumably lower the risk of herdmates acquiring new S. aureus intramammary infection, then povidone-iodine appears to be the better of the two methods. No difference in total milk production between lactation one and two in either group was found, suggesting that permanent loss of one quarter was not detrimental to overall milk production.